To get SSN number as quickly as possible you don't need to wait for the physical Green Card, absolutely not, just use the I-551 stamp in the passport. Apply for SSN card in the SSA office. In the SSA Office fill out the form and give the address you want you SSN card to be sent.
You can visit the SSA office as soon as you arrive in Miami. You can skip the visit to the SSA office, but if you decide to wait it can take much more time for the SSN card to arrive, which means doing nothing, walking around, enjoying the sunny weather...
As for the GC - you'll just have to wait !!
Yes it will arrive to the address you provide, it is all based on addresses that you provide.
At the POE (first US airport) you give the address for GC (if it is different from the one given in the embassy, CO) and in SSA Office you give an address where you want the SSN card to arrive. The address given in SSA office does not have to be the same as the one for GC. Take the passport (and a copy of first page and stamp) and bring to SSA office.
The level of training in each SSA will determine how efficiently they handle the request for SSN card.
Use 1-155 stamp to apply for driver's license.
If you have international driver's license from home country you can use it temporarily in US.
Furthermore, car insurance reduction is calculated on the basis of driver's license, of "a driving experience". Based on your driver's license if you pass the driving tests it is possible to obtain two month temporary driver's license.
You cannot apply for drivers license if you don't have your SSN.
here is the link to the web site:
http://answers.yahoo.com/question/index?qid=20100609155151AABZ7gI
The information on that yahoo link is not quite accurate, plus it's about 3 years old anyway.
I live in California, and I know for a fact that there are instances where a DL can and will be issued without a SSN. Here's a direct link to the CA DMV's site that specifically addresses the issue of SSN and DL:
http://www.dmv.ca.gov/pubs/brochures/fast_facts/ffdl08.htm
To the OP: if you need to apply for a DL immediately, visit the nearest SSA with your passport which should have the I-551 stamp on it and apply for the SSN. You will most likely already be in the system, in which case you can ask them to tell you your SSN (while you wait to receive the physical card in the mail). Write down the number you're provided with and use this number to fill out your DL application form at the DMV office. You do not need to provide a physical copy of the SSN card (unless you're applying for a Commercial DL).